Nearly 140,000 Vietnamese nationals have signed a petition urging the Obama administration to launch an independent investigation into "an environmental disaster" that caused mass fish kills along Vietnam's central coast.

The move comes as the Southeast Asian country struggles to identify exactly who or what left millions of fish dead and many livelihoods impacted.

On the White House-run "We the People" website, an unidentified petitioner claiming to be from Ha Tinh, one of the hard-hit areas, called on the U.S. to "provide independent assessment of a steel plant" at the heart of the controversy.

Formosa Plastics is cited in the petition, although a probe called by Hanoi officials has yet to link the massive fish kill to a $10.6 billion steel plant run by the Taiwanese-based conglomerate in Ha Tinh.

Formosa representatives did not respond to VOA requests seeking comments about criticism targeting their company before publication.

A preliminary investigation of the mysterious marine-life catastrophe, announced by Vietnam's environmental watchdog, blamed red tide — a phenomenon known as an algal bloom — and poisonous chemicals in wastewater as the two main factors.

Call for ‘investigators from outside’

Well-known anti-China activist Le Anh Hung, who is based in Hanoi, said he signed the petition after "losing trust in the morality and objectivity of Vietnamese agencies."

FILE - Vietnamese protesters take to the street during a rally denouncing recent mass fish deaths in Vietnam's central province, in Hanoi, Vietnam, May 1, 2016.

"That is why we need independent investigators from outside, especially from the U.S. government," he said. "I want to hear a positive response from the White House."

Tuesday's call for a White House probe comes just weeks before President Barack Obama makes his first visit to Vietnam, and it is unclear whether he will mention this petition in meetings with Vietnamese officials.

"We The People," the White House-run site, says petitions that gather 100,000 signatures in 30 days will be reviewed to ensure "it gets in front of the appropriate policy experts, and issue an official response."

At the end of 2014, the Obama administration responded to a petition signed by more than 130,000 Vietnamese about imposing sanctions on China for bringing a giant oil rig into waters claimed by Vietnam, an incident that plunged Hanoi-Beijing relations to its lowest point in years.

Pressure from within

While some Vietnamese find hope in the country situated half a world away, activist Ngo Duy Quyen said it is unrealistic to seek help from foreign entities.

"It is, of course, a good way to gather international support, but the pressurization on the authorities should come from within, and that can be done through street protests," he said.

To make his voice heard, Quyen joined hundreds of people who took to the streets of numerous Vietnamese cities Sunday, shouting slogans and holding banners aimed at Formosa in a series of rare protests in the Communist country.

Prior to the Sunday marches, hundreds of desperate fishermen in hard-hit provinces dumped dead fish on the national highways and used fishing net and boats to block traffic.

Vietnamese state-run media have carried out extensive coverage of the massvie fish deaths, but stayed silent about the demonstrations. International news outlets reported small scuffles between protesters and police.

Vietnamese authorities later said they arrested two members of anti-state organizations, allegedly for inciting the rallies.

Do Hoang Diem, chairman of the U.S.-based pro-democracy group Viet Tan, which is unsanctioned in Vietnam, said it is not the first time his organization become Vietnam's target, adding that everyone in the country should be allowed to freely express themselves.